Engine technology thread.

[serialk11r]

Yikes I just noticed cams are expensive.

I guess waiting to see what they add to the BRZ STI is probably a better idea, for people who can wait. Changing valves, springs, cams, rods, pistons, etc. easily will add up to a crapton of money.

I also just noticed that from EJ20 to FB20 they narrowed the valve angle...for the FA if they decided to make any changes it could affect the geometry :O

[Homemade WRX]

Originally Posted by arghx7

If you put in more aggressive cams in terms of lift and duration, you could probably find a way to make it work. There isn't a whole lot else to say without more specs on the actual engine.

Completely agree on the underlined part. As a note for long duration and higher lift cams with cam phasing. I know I've run into piston clearance limitations with my EJ motors. I mechanically limit the travel the cam gear has as a safety measure. Most of my hi-RPM guys just ditch it as they are targetting an area of the curve where AVCS stays at full retard...

...I know, 'never go full retard'

Originally Posted by serialk11r

Yikes I just noticed cams are expensive.

NA builds are expensive for what power you get in return vs. that of FI...hence why all that FI talk was going on. Don't need cams for FI until you're well past the NA limits (usually).

[Dimman]

Originally Posted by serialk11r

Yikes I just noticed cams are expensive.

I guess waiting to see what they add to the BRZ STI is probably a better idea, for people who can wait. Changing valves, springs, cams, rods, pistons, etc. easily will add up to a crapton of money.

I also just noticed that from EJ20 to FB20 they narrowed the valve angle...for the FA if they decided to make any changes it could affect the geometry :O

For lift:valve a 'rule of thumb' .25D or more the valve is usually no-longer the restriction. Then we see even more lift than that at max on performance motors, because a cam's max lift is only pretty-much instantaneous.

(low-lift the perimeter of the valve is the air restriction, at over .25D (or was is .3D?) it is the area of the valve/port area minus valve stem that matters)

So in the 2GR's case with the 5.99mm intake lift and 34.5mm valves, it looks like there is some room for power gains with just higher lift.

[Syldrin]

Originally Posted by Homemade WRX

^^you hit the nail on the head!

I have a saying...
You have clean (emissions), powerful and fuel efficient; pick two.

it's more like pick one man lol.

[serialk11r]

Wait fully retarded intake? What about scavenging? I don't know how accurate the online guides to racing cams are but the physics seems more or less valid. For the FRS engine the intake duration could be quite a bit longer as it is tuned for high end power afterall, but just looking at the 3GR-FSE case, it appears that there is some missing potential in several spots in the powerband. Although I suppose the 3GR (and 2GR) are more for low end torque.

Also on the subject of valve lift, why raise the valve higher than you need to instead of just "cutting" the peak of the cam lobe? Is it to keep the valve from floating? Seems like unnecessary friction.

[Dimman]

Originally Posted by serialk11r

Wait fully retarded intake? What about scavenging? I don't know how accurate the online guides to racing cams are but the physics seems more or less valid. For the FRS engine the intake duration could be quite a bit longer as it is tuned for high end power afterall, but just looking at the 3GR-FSE case, it appears that there is some missing potential in several spots in the powerband. Although I suppose the 3GR (and 2GR) are more for low end torque.

Also on the subject of valve lift, why raise the valve higher than you need to instead of just "cutting" the peak of the cam lobe? Is it to keep the valve from floating? Seems like unnecessary friction.

Floating issue I think. Acceleration on the valves. Ramp rates is the term I think.

[serialk11r]

Do typical high lift valves have greater ramp rates? (forgive me if that's incorrect usage, I mean peak valve acceleration) If they don't there's no need to have a significantly higher peak...

[Dimman]

Originally Posted by serialk11r

Do typical high lift valves have greater ramp rates? (forgive me if that's incorrect usage, I mean peak valve acceleration) If they don't there's no need to have a significantly higher peak...

Not something I know too much about. But think of how much time /degrees you have to go from 0 to say 9mm of lift. So the valve has to open fast. Now if you just cut it off 'flat' at max lift over and maintain it, the curve is going to look like it wants to 'throw' the valve off the cam/lifter. Does that make any sense?

[serialk11r]

Yes, but if the valve isn't "thrown" off at the peak, simply extending the length of the peak would not cause the valve to float.

[Homemade WRX]

Originally Posted by serialk11r

Wait fully retarded intake? What about scavenging?

Retarded in regards to cam phase adjustment. Doesn't mean no overlop, though I bet it does from the factory (emissions).

Originally Posted by Dimman

Ramp rates is the term I think.

Ramp rates, yup.

Originally Posted by serialk11r

Do typical high lift valves have greater ramp rates? (forgive me if that's incorrect usage, I mean peak valve acceleration) If they don't there's no need to have a significantly higher peak...

I'll try to keep things simple since cams are a component that has their own specialists.

Ramp rate is slimply the amount of lift over degrees and you'll see its a curved slope. From this and engine speed, we can derive velocity and acceleration of the valvetrain components. We can then work out the forces and so on to properly design components.
Now if you were to take given lobe and simply increase duration and lift equally (10% for instance), you'd keep the same curve however velocity and acceleration are going to be higher for the same given engine speed. Further distance to travel in the same 720 degrees.

Now you'll notice on race cams and good performance cams that the lobe is assymetrical. This is because you want to open the intake as fast as possibly and stay there as long as you can. However if you approach the nose too quickly, you'll float the valve and you'll find a hard stop at a piston (bad joojoo) or at coil bind (good way to break a spring and drop a valve = toasted engine)
Now on the exhaust side, you'll see it is a much steeper ramp rate while not allowing the valve to drop so fast that it leaves contact of the cam. If it does, you'll get bounce off of the seat. This is another good way to break things. It'll tear a valve and the head will fall into the engine, or you'll beat the seat back into the head, decrease your lash, which will probably end up leading to a wiped lobe or another failed component in the valvetrain (depends on style of valvetrain).

[Dimman]

Originally Posted by Homemade WRX

Completely agree on the underlined part. As a note for long duration and higher lift cams with cam phasing. I know I've run into piston clearance limitations with my EJ motors. I mechanically limit the travel the cam gear has as a safety measure. Most of my hi-RPM guys just ditch it as they are targetting an area of the curve where AVCS stays at full retard...

...I know, 'never go full retard'


NA builds are expensive for what power you get in return vs. that of FI...hence why all that FI talk was going on. Don't need cams for FI until you're well past the NA limits (usually).

What are the included angles and diameters on the EJs?

If we have a narrower angle there is less chance to bang into the piston, right?

[Homemade WRX]

Originally Posted by Dimman

What are the included angles and diameters on the EJs?

If we have a narrower angle there is less chance to bang into the piston, right?

Which EJ head? There are LOTS.

yes, narrower angle means that you have less chance of valve to valve or should I say you can have a later exhaust closing/earlier intake opening for the same given valve diameter. The issue with less included angle is you tend to have smaller valves.

The valve to piston is completely dependent on geometry, rod ratio, etc. Though I would say as a generality, yes.

[serialk11r]

Terribly sorry about momentary topic jump:
I looked back to the chart arghx7 provided on exhaust pressure, after seeing that the exhaust valve opens ~45 degrees before BDC, and went over to the chart provided here on efficiency/flow vs rpm, the only "turbine map" I can find:
http://www.turbodriven.com/en/turbof...gnTurbine.aspx
That turbine spins to about 180krpm, pretty typical.

In the chart arghx7 kindly provided, it appears that the engine is supercharged. However the exhaust valve opens precisely at BDC, which is atypical, and the extra expansion removes some quantity of the pressure, so I think scaling the peaks to 2.5 bar would be representative of a high performance NA motor.

The green lines on the chart should be mass flow and red should be efficiency since mass flow strictly increases with pressure and efficiency doesn't. Okay so now the lines are quite short, and we see that if the pressure ratio is low the efficiency is low. Higher rpm than ideal at the same pressure ratio has lower efficiency, but this is because flow would be higher, and there would be some more restriction so the gases hitting the turbine would be slower. So it appears that this turbine that does best at about 2.4 pressure ratio, 160krpm, can still operate at >60% efficiency (that's >85% of peak efficiency) at pressure ratio of 1.8. The greater the pressure, the greater the flow, and we see that almost all of flow happens when the pressure is >1.8 bar in the diagram, as crank angle directly corresponds to time. It seems that overall, the useful kinetic energy in the exhaust can be captured at >50% efficiency with a turbine! As I calculated before, that's worth ~12hp on a 200hp motor. If backpressure increases to say, 0.5bar, that costs the motor 5hp, but the turbine can pick up around half of that for a net 10hp gain.

5% power increase for just a turbine and a mechanical link to the engine is pretty good imo. At lower speed the turbine becomes useless, but volumetric efficiency also sucks at low engine speeds without variable duration intake so it doesn't matter. Side benefit may be being able to go for lighter muffler and still have low noise?

[arghx7]

Originally Posted by serialk11r

Terribly sorry about momentary topic jump:
I looked back to the chart arghx7 provided on exhaust pressure, after seeing that the exhaust valve opens ~45 degrees before BDC, and went over to the chart provided here on efficiency/flow vs rpm, the only "turbine map" I can find:
http://www.turbodriven.com/en/turbof...gnTurbine.aspx
That turbine spins to about 180krpm, pretty typical.

In the chart arghx7 kindly provided, it appears that the engine is supercharged. However the exhaust valve opens precisely at BDC, which is atypical, and the extra expansion removes some quantity of the pressure, so I think scaling the peaks to 2.5 bar would be representative of a high performance NA motor.

The green lines on the chart should be mass flow and red should be efficiency since mass flow strictly increases with pressure and efficiency doesn't. Okay so now the lines are quite short, and we see that if the pressure ratio is low the efficiency is low. Higher rpm than ideal at the same pressure ratio has lower efficiency, but this is because flow would be higher, and there would be some more restriction so the gases hitting the turbine would be slower. So it appears that this turbine that does best at about 2.4 pressure ratio, 160krpm, can still operate at >60% efficiency (that's >85% of peak efficiency) at pressure ratio of 1.8. The greater the pressure, the greater the flow, and we see that almost all of flow happens when the pressure is >1.8 bar in the diagram, as crank angle directly corresponds to time. It seems that overall, the useful kinetic energy in the exhaust can be captured at >50% efficiency with a turbine! As I calculated before, that's worth ~12hp on a 200hp motor. If backpressure increases to say, 0.5bar, that costs the motor 5hp, but the turbine can pick up around half of that for a net 10hp gain.

5% power increase for just a turbine and a mechanical link to the engine is pretty good imo. At lower speed the turbine becomes useless, but volumetric efficiency also sucks at low engine speeds without variable duration intake so it doesn't matter. Side benefit may be being able to go for lighter muffler and still have low noise?

you're kind of taking that chart out of context... it was a study on boosted engines and exhaust gas interference